1. Field of the Invention
This invention relates generally to an artificial illumination control system for photographic apparatus and, more particularly, to an artificial illumination control system for quenching a strobe subsequent to the expiration of a select time delay after the shutter is commanded to close, which time delay is progressively decreased in correspondence with increasing ambient scene light intensity.
2. Description of the Prior Art
Electronic photographic strobe devices of the type in which the flashlight produced by the flash tube of the device is automatically terminated after a predetermined quantity of light has been received from the scene being photographed by a light-responsive control portion of the device are well known in the art. Such strobes are commonly referred to as quench strobes. In addition to having an independent light-responsive control circuit in the strobe, it is also well known to utilize the exposure control circuit associated with the actual camera apparatus to control the firing and quenching of a strobe unit as is more fully disclosed in U.S. Pat. No. 3,776,112, by Wilwerding issued 1973. Wilwerding discloses a circuit coupled to the light-integrating exposure control circuit of a camera to effect the flash quenching of an electronic flash unit. Thus, it is well known to couple an electronically controlled shutter camera with a quenchable electronic strobe unit so that the strobe unit is quenched simultaneously with the command signal to return the shutter blade elements to their closed position.
Such an arrangement however would not be compatible with an exposure control system of the type described in a copending application for U.S. patent Ser. No. 619,384 entitled "Exposure Control System With Fill-Flash Race Condition" by Edwin K. Shenk, filed Oct. 3, 1975. The aforementioned exposure control system is utilized in conjunction with a shutter blade arrangement of the so-called "scanning type" which embodies a pair of shutter blade elements, each of which includes a primary aperture therethrough to cooperatively define a gradually varying effective aperture size as a function of the position of the shutter blade elements. Each shutter blade element additionally includes a photocell sweep secondary aperture which apertures also cooperatively define a gradually varying effective secondary aperture in front of the exposure control photocell as a function of blade position. The photocell sweep secondary apertures are generally configured to progressively open ahead of the primary aperture so that the exposure control circuit effects the closing of the shutter blade elements at a time prior to which the film is fully exposed. Prematurely signalling the shutter blade elements to close prior to the time required for a full film exposure anticipates for the additional scene light which will impinge upon the film during the finite time required for the shutter blade elements to fully close. Thus, quenching the strobe solely as a function of the exposure control system command signal to initiate closing of the shutter blade elements as disclosed in U.S. Pat. No. 3,776,112, supra will result in an under-exposure since the srobe is quenched almost instantaneously. In order to compensate for the underexposure, it is suggested in a copending application for U.S. patent Ser. No. 674,840 by G. D. Whiteside and B. K. Johnson filed Apr. 8, 1976, that the actual quench signal be delayed by a predetermined time delay which correlates to the anticipation characteristic of the photocell secondary apertures. Such a time delay provides for satisfactory exposures in situations where the ambient scene light intensity is so low that the photographer would customarily utilize either a flashbulb or strobe. In situations where the ambient scene light intensity is high, and particularly, where the subject is framed against a lighted background, it may still be desirable to utilize a flashlamp or strobe in order to adequately expose the features of the subject. However, in such "fill-in" flash situations, the predetermined time delay may result in overexposing the subject since the subject is already partially illuminated by the lighted background.
Thus, it is suggested in a copending application for U.S. patent Ser. No. 684,902 by G. D. Whiteside and B. K. Johnson filed concurrently herewith, that the artificial illumination control system selectively vary the time delay at which the strobe is quenched subsequent to the command signal to close the shutter as a function of whether the camera operates in a "fill-in" flash mode or an ordinary flash mode. However, during the "fill-in" flash mode of operation, there may be a great variance in the background light intensity between different photographic scenes. An increase in the background light intensity may also increase the illumination of the photographic subject thereby requiring less reflected strobe light to adequately illuminate the subject. Delaying the strobe quench for only a single select time period for all "fill-in" flash mode type exposures may not be sufficient to accommodate for all the variations in background light intensity which may be encountered.
Thus, it is a primary object of this invention to provide an artificial illumination control system for progressively decreasing the time delay at which the strobe is quenched, subsequent to the command to close the shutter, as a function of increasing ambient scene light intensity so that the shutter admits progressively less reflected strobe light during the finite time required for the shutter to close.
Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the mechanism and system possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.